Visualization of NMDA receptor-induced mitochondrial calcium accumulation in striatal neurons.
Ca2+ influx through NMDA receptor-gated channels and the subsequent rise in intracellular Ca2+ concentration ([Ca2+]i) have been implicated in cytotoxic processes that lead to irreversible neuronal injury. While many studies have focused on cytosolic Ca2+ homeostasis, much less is known about Ca2+ fluxes in subcellular organelles, such as mitochondria. The mitochondria play an important role in Ca2+ homeostasis by sequestering cytosolic Ca2+ loads. However, mitochondrial Ca2+ overload can impair ATP synthesis, induce free radical formation, and lead to lipid peroxidation. Thus, it is also important to understand the mitochondrial Ca2+ fluxes induced by NMDA. In this study, changes in mitochondrial Ca2+ concentration ([Ca2+]m) in cultured striatal neurons were monitored with a Ca(2+)-binding fluorescent probe, rhod-2, and laser scanning confocal microscopy. The rhod-2 fluorescence signal was highly localized in mitochondrial areas of confocal images. A rapid increase of [Ca2+]m was observed when neurons were treated with 100 microM NMDA. The increased [Ca2+]m induced by NMDA could not be observed in the presence of ruthenium red, an inhibitor of the mitochondrial Ca2+ uniporter, or CCCP, a protonophore that breaks down the mitochondrial membrane potential necessary for Ca2+ uptake. The magnitude and reversibility of changes in [Ca2+]m induced by NMDA were variable. In neurons receiving multiple pulses of NMDA, [Ca2+]m did not return to baseline. The elevated [Ca2+]m may persist indefinitely and may rise further after successive NMDA exposures. These data demonstrate that Ca2+ accumulates in mitochondria in response to NMDA receptor activation. This Ca2+ accumulation may play a role in the excitotoxic mitochondrial dysfunction induced by NMDA.
Peng
T I
TI
Department of Neurology, Emory University School of Medicine, Atlanta, Georgia 30322, USA.
Jou
M J
MJ
Sheu
S S
SS
Greenamyre
J T
JT
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D003342:Corpus Striatum / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D005456:Fluorescent Dyes; D006575:Heterocyclic Compounds, 3-Ring; D007476:Ionophores / Q000494:pharmacology; D018613:Microscopy, Confocal; D008928:Mitochondria / Q000378:metabolism*; D016202:N-Methylaspartate / Q000494:pharmacology; D009474:Neurons / Q000378:metabolism*; D009994:Osmolar Concentration; D051381:Rats / Q000196:embryology; D017207:Rats, Sprague-Dawley; D016194:Receptors, N-Methyl-D-Aspartate / Q000502:physiology*; D012430:Ruthenium Red / Q000494:pharmacology
D005456:Fluorescent Dyes; D006575:Heterocyclic Compounds, 3-Ring; D007476:Ionophores; D016194:Receptors, N-Methyl-D-Aspartate; C068483:rhod-2; D012430:Ruthenium Red; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D016202:N-Methylaspartate; D002118:Calcium